Disposable, absorbent paper products have been developed to replace more conventional cloth products. These products include facial tissues, paper towels, towels, and wipers or wipes. The wipers or wipes may be intended primarily for use in commercial, industrial, or other harsh and/or demanding applications requiring strength.
For many applications, disposable absorbent paper products ideally simulate cloth in appearance, perception, and performance. Desirable physical properties include softness, strength, stretchability, absorbency, ability to wipe dry, bulk, and resistance to abrasion. The properties required of a wipe will depend on the intended use of the product. Softness is a desirable property for most absorbent paper products. End users find soft products more pleasant to handle. The softness also enables products to conform to the shape that is required by the application. Strength and stretchability are other desirable properties, particularly for products that are to be used for industrial applications.
It may also be desirable for a product to have good abrasion resistance, if it is to be used for wiping, scouring, or cleaning. Even for facial tissue, poor abrasion resistance can result in pilling or dusting of fibers from the tissue when handled by the consumer. Bulk is also important as it enables the paper web product to resemble cloth in feel, and also because it generally adds to softness and absorbency.
Some paper web properties are often inversely related. An increase in one may often be accompanied by a decrease in the other. In one example, an increase in web density or fiber concentration increases the ability of the web to wipe dry or pick up moisture, due to increased capillary action within small spaces between the fibers. Unfortunately, the increase in closeness of the fibers also decreases the space between the fibers that is available for holding moisture, thereby reducing the absorbency of the product. Strength and softness may also be inversely related. Methods which produce soft paper often result in strength reduction. This is generally true because the principal source of web strength is the inter-fiber bonds formed by the hydrate bonding processes associated with papermaking. Paper having a heavy concentration of these bonds is generally stiff. To soften the paper, it is generally necessary to reduce the stiff bonds, which often results in a loss of strength.
One method commonly used to reduce the stiff papermaking bonds is to crepe the paper from a drying surface using a doctor blade, thereby disrupting and breaking many of the inter-fiber bonds in the paper web. Other methods used to reduce the bonds include chemical treatment of the papermaking fibers to further reduce the inter-fiber bonding capacity. These methods generally reduce the strength of the papermaking bonds.
Some processes restore the strength loss by reducing the papermaking bonds, by adding bonding materials to the web. The bonding materials are capable of adding strength more than they add stiffness. In one method, the bonding material is added to the aqueous slurry of fibers and deposited on the web forming surface along with the fibers. This method, however, reduces the absorbency of the web as it fills the pores between the fibers with bonding material.
In another method, bonding material is applied to the web in a spaced apart, geometrically regular pattern on the web. In this method, the majority of the web surface is free of the bonding material, leaving the majority of the surface highly absorbent. As the papermaking fibers are often less than about one quarter of an inch long, it is often desirable to have the bonding material applied in a pattern, repeated at intervals less than the average papermaking fiber length. Any harshness in the bonded areas may be reduced by tightly adhering the bonded portions of the web to a creping surface and removing the web with a doctor blade, thereby finally creping the bonded portions to soften those portions of the web.
Attempts have been made to apply decorative or commercial messages onto paper web products, including those products strengthened with patterns of bonding material. In one method, larger, foreground patterns have been printed with ink onto paper web products. In one such method, the decorative patterns are printed with ink in a secondary process, after the paper web products have been previously printed with bonding material background patterns and creped, in a primary process. The secondary printing process requires further processing the web, including running the web through additional rolls and nips. The secondary process also requires additional capital equipment, processing time, and labor. In addition, the secondary process can compress the printed web, at least partially degrading desirable properties, such as softness and bulk, which were previously imparted by the primary process.
The printed ink designs made using the secondary process are often not colorfast, and may run. In some applications, wipes may be used for commercial purposes, such as cleaning products for sale, or cleaning commercial buildings for use. Industrial or cleaning solvents may be used with the wipes. The wipes, which may also be laden with aggressive solvent, can cause the logo ink color to be left behind on the wiped commercial products and commercial building surfaces. This is undesirable.
What would be desirable, is a method for forming large patterns onto paper web products which are also strengthened with bonding material, without causing the pattern colors to bleed over the surfaces wiped. It would be most advantageous to form the logo pattern and any background pattern in the same process, not requiring a second printing step.